JUNG JESSICA has been working on cases since she was 18. Always the best investigator in the company, she was always envied and admired. Intelligent and beautiful, she seemed to have it all. 

ZHANG YIXING wasn't really an investigator. In fact, he was only the doctor that was assigned to go along with the investigators in case one got injured. Always shy and introverted, he never really had his chance to show that he was much more smarter than he seems.

LU HAN was one of the most hated investigators. He was a jerk at heart, but he was very intelligent and a player with the ladies. He knew how to work his way around cases and was very much one of the top investigators in the business.

HUANG ZITAO is only a beginner, but he's smart. As a young man with huge anger issues, he's usually seen in a fight with others. However, he's one hell of an investigator.

So far, Jung Jessica has worked on 300 cases, Yixing has helped in 120 cases, Lu Han has worked on 220, and Tao has worked on 25. On November 21st, the company decides to place all four in one huge case: case #666. They are sent to Hyunjo Island and are to investigate the mysterious murder of Miss Hwang Tiffany. However, something seems to go on in the Hwang household, and the four investigators must work together to solve this case.